Digital Television Closed Captioning (DTVCC), formerly known as Advanced Television Closed Captioning (ATVCC), is the migration of the closed-captioning concepts and capabilities developed in the 1970's for National Television System Committee (NTSC) television video signals to the high-definition television environment defined by the Advanced Television (ATV) Grand Alliance and standardized by the Advanced Television Systems Committee (ATSC). This new environment provides for larger screens, higher screen resolutions, enhanced closed captions, and higher transmission data rates for closed-captioning. The Electronic Industries Alliance publication EIA-708 is the standard for closed captioning for ATSC television streams in the United States and Canada. The U.S. Federal Communications Commission (FCC) regulations require EIA-708 caption decoders in all 13-inch (33-cm) diagonal or larger digital televisions. Furthermore, the FCC regulations require some broadcasters to caption a percentage of their broadcasts.
EIA-708 captions for DTV provide for different carriage methods before and after the encoder. The EIA-708 captions may be carried on a serial data link (RS232) from a caption server to the encoder as specified in Society of Motion Picture and Television Engineers (SMPTE) 333M, or embedded in a caption distribution packet (CDP) in serial digital video vertical ancillary (VANC) data for recording and distribution as specified in SMPTE 334M. High-Definition (HD) program distribution from networks to affiliates or member stations usually use compressed video over satellite. Therefore, the program must extract captions and place them in private data packet identifier (PID) or A/53B video user data. Different video programs have different DTVCC carriage, and an HD encoder should be able to extract captions from both caption carriage methods and handle carriage switch on the fly. Due to the different way of capturing and organizing the captions of SMPTE 333M and SMPTE 334M, the unpredictable switch between SMPTE 333M and SMPTE 334M can cause capture buffer underflow and impact the EIA-708 caption distribution.
Thus, there is a demand for a buffer control method and system that handles unpredictable caption carriage switch to improve the efficiency of caption distribution. The presently disclosed invention satisfies this demand.